Amide formation is a fundamental reaction in chemical synthesis (1). The importance of amides in chemistry and biology is well recognized and has been studied extensively over the past century (2-4). Although several methods are known for the synthesis of amides, preparation under neutral conditions and without generation of waste is a challenging goal (1, 5). Synthesis of amides is mostly based on activated acid derivatives (acid chlorides, anhydrides) or rearrangement reactions induced by acid or base which often involve toxic chemical waste and tedious work-up (5). Transition-metal catalyzed conversion of nitrites into amides was reported (6, 7, 8). Catalytic acylation of amines by aldehydes in the presence of a stoichiometric amount of oxidant and a base is known (9, 10). Recently, oxidative amide synthesis was achieved from terminal alkynes (11). Cu(I) catalyzed reaction of sulfonyl azides with terminal alkynes is a facile method for the synthesis of sulfonyl amides (12, 13).
The applicants of the present invention recently reported the dehydrogenation of alcohols catalyzed by PNP— and PNN—Ru(II) hydride complexes (14). Whereas secondary alcohols lead to ketones (15, 16), primary alcohols are efficiently converted into esters and dihydrogen (14-16). The dearomatized PNN pincer complex 1 (FIG. 1) is particularly efficient (17); it catalyzes this process in high yields under neutral conditions, in the absence of acceptors or promoters.
Given the widespread importance of amides in biochemical and chemical systems, an efficient synthesis that avoids wasteful use of stoichiometric coupling regents or corrosive acidic and basic media is highly desirable.